Impact of microplastics on gut microbiota diversity and immune response in freshwater fish species (Zoology)

Project Abstract

Microplastics (MPs) have emerged as pervasive contaminants in aquatic ecosystems, with freshwater systems showing increasing concentrations that threaten biodiversity and ecosystem services. This study investigates how chronic exposure to environmentally relevant concentrations of microplastics influences gut microbiota diversity and the immune competence of key freshwater fish species, integrating microbiome profiling, immunological assays, and physiological endpoints. A multi-species approach was employed, selecting representative omnivorous and carnivorous freshwater fish to assess interspecific variability in response to MPs. Fish were exposed to polystyrene and polyethylene microplastics at low, medium, and high concentration regimes for 12 weeks under controlled laboratory conditions, alongside appropriate sediment and dietary controls to simulate natural exposure routes including ingestion and trophic transfer. Gut microbiota composition was characterized using 16S rRNA gene sequencing to evaluate alpha and beta diversity, taxonomic shifts at phylum and genus levels, and predicted functional pathways via PICRUSt2. Immune status was assessed through quantification of innate and adaptive immune markers, including mucosal immunoglobulins, cytokine expression (TNF-?, IL-1?, IL-10), respiratory burst activity, and complement system components. Physiological metrics encompassed growth performance, condition factor, hepatic detoxification enzyme activities (e.g., GST, SOD, CAT), and histopathological evaluation of intestinal tissues to detect barrier integrity disruption. The study further investigates the potential mechanistic links between MP-associated microbiome alterations and immune modulation, exploring whether dysbiosis correlates with elevated pro-inflammatory cytokines, impaired short-chain fatty acid production, or altered antimicrobial peptide expression. Data were analyzed using mixed-effects models to account for random tank effects and species-specific responses, followed by multivariate redundancy analysis to identify microbiome-immune associations. Anticipated findings include a dose-dependent enrichment of potential opportunistic taxa (e.g., opportunistic pathogens) and a concomitant reduction in commensal, SCFA-producing bacteria, accompanied by heightened mucosal inflammation and systemic immune activation in MP-exposed groups. Differences between species are expected to reflect innate immune strategy and gut morphology, potentially revealing differential susceptibility linked to feeding ecology and microbiome resilience. The study contributes to the broader understanding of how microplastics modulate host health via gut microbial networks and immune pathways, emphasizing the ecological relevance for freshwater fish populations and aquaculture systems. Outcomes will inform risk assessment, guide environmental policy on microplastic pollution, and propose mitigation strategies such as improved wastewater management and the development of MP-resistant feed formulations. By integrating microbiome analytics with immunophysiology and histopathology, this research delineates a comprehensive framework to elucidate the cascading effects of microplastics from the microbial level to whole-organism health, highlighting critical thresholds beyond which compensatory immune responses fail and vulnerability to disease increases in freshwater ichthyofauna.

Project Overview

What This Project Is About

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The project explores how tiny plastic pieces in the water, called microplastics, affect the gut bacteria of freshwater fish and how this may change their immune system. It looks at changes in gut microbial diversity and how the fish respond to infections or stress.

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The Problem It Addresses

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Microplastics are widespread in rivers and lakes, and they can carry pollutants and disrupt animal digestion. Little is known about how these plastics alter the gut ecosystem of fish and what that means for their health and disease resistance.

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Objectives of the Project

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1. Describe the gut microbiota composition of model freshwater fish under normal and microplastic exposure.
2. Assess changes in immune-related markers and overall health indicators.
3. Identify potential links between microbiota shifts and immune responses.
4. Evaluate dose and exposure time effects on gut health and immunity.

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What You Will Do Step by Step

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1. Conduct a literature review to understand current knowledge and gaps.
2. Collect water samples with and without microplastics for a controlled setup.
3. Expose freshwater fish to defined microplastic concentrations in a controlled aquarium system.
4. Sample gut contents at set intervals to analyze microbial communities (basic sequencing or microscopy).
5. Measure immune-related indicators (e.g., inflammatory markers, white blood cell counts).
6. Compare health outcomes between exposed and control groups.
7. Analyze data for correlations between microbiota changes and immune responses.
8. Discuss implications for fish health and environmental management.

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Expected Outcome

We expect to find measurable shifts in gut bacteria composition and some changes in immune markers in fish exposed to microplastics, with possible links between specific microbes and immune responses. The study should provide insight into how pollution can affect fish health and help inform environmental risk assessments and policy decisions.